U.S. patent application number 10/889677 was filed with the patent office on 2005-01-13 for organic electroluminescent element.
Invention is credited to Mori, Toshitaka, Ohyagi, Yasuyuki.
Application Number | 20050007016 10/889677 |
Document ID | / |
Family ID | 32866804 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050007016 |
Kind Code |
A1 |
Mori, Toshitaka ; et
al. |
January 13, 2005 |
Organic electroluminescent element
Abstract
In an organic electro luminescent element, an organic layer and
an electron injecting layer are inhibited from being oxidized, and
alleviated in damage caused by the sputtering during manufacture.
Thereby, an organic electroluminescent element that takes out light
with high efficiency from a cathode of a top side and is capable of
displaying a high quality image can be provided. An organic
electroluminescent element according to the present invention
includes at least a base material, an anode, an organic
electroluminescent layer, a conductive protection layer having the
optical transparency and a cathode having the optical transparency
all of which are formed sequentially on the base material, wherein
the conductive protection layer is made of a metal or a metal and a
metal oxide thereof.
Inventors: |
Mori, Toshitaka; (Tokyo,
JP) ; Ohyagi, Yasuyuki; (Tokyo, JP) |
Correspondence
Address: |
SEYFARTH SHAW
55 EAST MONROE STREET
SUITE 4200
CHICAGO
IL
60603-5803
US
|
Family ID: |
32866804 |
Appl. No.: |
10/889677 |
Filed: |
July 13, 2004 |
Current U.S.
Class: |
313/512 ;
313/113; 313/504; 313/506; 428/332; 428/690; 428/917 |
Current CPC
Class: |
H01L 51/5221 20130101;
H01L 2251/5315 20130101; H05B 33/26 20130101; H01L 51/5092
20130101; Y10T 428/26 20150115 |
Class at
Publication: |
313/512 ;
313/504; 313/506; 313/113; 428/690; 428/917; 428/332 |
International
Class: |
H05B 033/12; H05B
033/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2003 |
JP |
2003-195343 |
Claims
What is claimed is:
1. An organic electroluminescent element, comprising at least a
base material and, sequentially formed from the base material side,
an anode, an organic electroluminescent layer, a conductive
protection layer having the optical transparency and a cathode
having the optical transparency, wherein the conductive protection
layer is made of a metal or a metal and a metal oxide thereof.
2. The organic electroluminescent element according to claim 1,
wherein a metal used in the conductive protection layer, with
extinction coefficient of the metal as k, a film thickness as d and
a wavelength as .lambda., is in the range of
0.ltoreq.k.times.d<0.11.lambda..
3. The organic electroluminescent element according to claim 1,
wherein the metal oxide contained in the conductive protection
layer has a band gap of 2.9 eV or more.
4. The organic electroluminescent element according to claim 1,
wherein the conductive protection layer is constituted of at least
one kind of metals selected from a group consisting of zinc, tin,
lead, indium, gallium, magnesium and aluminum, or a combination of
at least one kind of the metals and at least one kind of the metal
oxides thereof.
5. The organic electroluminescent element according to claim 1,
wherein the cathode is made of a conductive oxide and has a
thickness in the range of 10 to 500 nm and the light transmittance
of 50% or more in a visible region of 380 to 780 nm.
6. The organic electroluminescent element according to claim 1,
wherein the sheet resistance of the cathode containing the
conductive protection layer is 20 .OMEGA./.quadrature. or less.
7. The organic electroluminescent element according to claim 1,
wherein the anode is made of any one of one kind or a combination
of two or more kinds of metals of a metal group having a work
function of 4.5 eV or more, or an alloy made of two or more kinds
of metals among the metal group, or one kind or two or more kinds
of a group of conductive inorganic oxides.
8. The organic electroluminescent element according to claim 7,
wherein the anode has a structure in which a layer made of the
metal or the alloy and a layer made of the conductive
inorganicoxide are laminated in this order from the base material
side and has the light reflectiveness.
9. The organic electroluminescent element according to claim 7,
wherein the anode is made of the metal or the alloy and has the
light reflectiveness.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an organic
electroluminescent element, in particular, an organic
electroluminescent element in which light can be taken out from a
cathode of a top side.
[0003] 2. Description of the Related Art
[0004] An organic electroluminescent element (hereinafter, referred
to as "organic electroluminescent element" or "organic EL element")
is advantageous in being high in the visibility owing to
self-emission, excellent in the impact resistance owing to being
all solid display different from a liquid crystal display device,
high in the response speed, not so much affected by a temperature
variation and wide in the angle of visibility. Accordingly, in
recent years, it is gaining attention in applications as a
light-emitting element in an image display device.
[0005] As a configuration of an organic EL element, with a
lamination structure of anode/light-emitting layer/cathode as a
basis, a configuration in which on a base material such as a glass
substrate a transparent anode is formed is usually adopted. In this
case, emitted light is taken out from a base material side (anode
side),
[0006] On the other hand, recently, in organic EL elements,
experiments of making a cathode transparent to take out emitted
light from a cathode side (top emission) are forwarded. When the
top emission is realized, firstly, in the case of both the cathode
and anode being made transparent, a light-emitting element that is
transparent as a whole can be realized. Since as a background color
of such a transparent light-emitting element, an arbitrary color
can be adopted, a display that is colorful other than during
emission can be realized, resulting in an improvement in the
decoration property. Furthermore, when the top emission is
realized, in the case of using a color filter layer or a color
conversion layer, on a light-emitting layer, each of the above
layers can be disposed. Still furthermore, since emitted light is
not blocked by a TFT (thin film transistor) of an active drive
display device, a display device high in the aperture ratio can be
realized.
[0007] As an example of an organic EL element in which the top
emission is realized by making a cathode transparent, a
configuration in which an organic layer including an organic EL
layer is interposed between an anode and a cathode, the cathode is
constituted of an electron injecting metal layer and an amorphous
transparent conductive layer, and the electron injecting metal
layer is in contact with the organic layer is disclosed (Japanese
Patent Application Laid-Open (JP-A) No. 10-162959).
[0008] Furthermore, a configuration in which in order to inhibit a
cathode material from diffusing to an organic layer that is an
organic EL layer, a Ca diffusion barrier layer is disposed between
a cathode and an organic layer to inhibit the short circuit and
deterioration of the characteristics of the organic EL element from
occurring is disclosed (JP-A No. 10-144957).
[0009] Still furthermore, as an example of double-sided emission, a
configuration in which in order to make a transparent cathode low
in the electric resistance, a conductive layer made of Ag, Mg or
TiN is interposed between a transparent cathode and an
light-emitting layer is disclosed (JP-A No. 10-125469).
[0010] Furthermore, a configuration in which in order to inhibit
oxygen and indium from invading or diffusing into an organic layer,
TiN is used in an anode is disclosed (JP-A Nos. 2002-15859 and
2002-15860).
[0011] However, in a conventional organic EL element that has
realized the top emission, it cannot be avoided that owing to
oxygen introduction in the process of forming a transparent cathode
or owing to release of oxygen from a target, an electron injecting
layer is oxidized. Accordingly, there are problems in that the
characteristics of the organic layer and the electron injecting
layer are deteriorated, and thereby high quality image display
cannot be obtained. Furthermore, in general, a transparent
electrode such as ITO (indium-tin oxide) is deposited by a
sputtering method. However, in the case of a transparent cathode
being formed by use of the sputtering method, there are problems in
that the organic layer including an organic EL layer and the
electron injecting layer are exposed to impact of sputtered
particles and Ar.sup.+ during the sputtering, and thereby the
emission characteristics are deteriorated.
SUMMARY OF THE INVENTION
[0012] The present invention is carried out in view of such
situations and intends to provide an organic electroluminescent
element in which an organic layer and an electron injecting layer
are inhibited from oxidizing and alleviated in damage of the
organic layer and the electron injecting layer caused by the
sputtering during formation of a transparent cathode, and thereby
light is efficiently taken out from a cathode of a top side and
high quality image display is realized.
[0013] In order to achieve such an object, the present invention
provides an organic electroluminescent element includes at least a
base material and, sequentially formed from the base material side,
an anode, an organic electroluminescent layer, a conductive
protection layer having the optical transparency and a cathode
having the optical transparency, the conductive protection layer
being made of a metal or a metal and a metal oxide thereof.
[0014] According to the invention, since a conductive protection
layer is formed into an optically transparent metal thin film that
is formed according to a vacuum deposition method in which oxygen
is not introduced in a deposition process, or an optically
transparent thin film made of a metal and a meta oxide thereof, the
organic layer and the electron injecting layer are inhibited from
being oxidized by oxygen not only in the deposition of the
conductive protection layer but also in the deposition of the
cathode having the optical transparency and alleviated in the
impact due to particles sputtered during the formation of the
cathode. As a result, an organic electroluminescent element less in
the leakage current and excellent in the emission characteristics
and the durability can be obtained. Further, by disposing a
conductive protection layer, an organic electroluminescent element
less in the deterioration of the characteristics, high in the
reliability and capable of taking out light with high efficiency
from a cathode of a top side and displaying high quality image can
be obtained.
[0015] In the present invention, it is preferable that a metal used
in the conductive protection layer, with extinction coefficient of
the metal as k, a thickness as d and a wavelength as .lambda., is
constituted so as to be in the range of
0.ltoreq.k.times.d<0.11.lambda..
[0016] Also in the present invention, it is preferable that the
metal oxide contained in the conductive protection layer is
constituted so that a band gap of the metal oxide is 2.9 eV or
more.
[0017] Also in the present invention, it is preferable that the
conductive protection layer is constituted of at least one kind of
metals selected from a group consisting of zinc, tin, lead, indium,
gallium, magnesium and aluminum, or a combination of at least one
kind of the metals and at least one kind of the metal oxides
thereof.
[0018] Also in the present invention, it is preferable that the
cathode is constituted so as to include a conductive oxide, have a
thickness in the range of 10 to 500 nm and be 50% or more in the
light transmittance in a visible region of 380 to 780 nm.
[0019] Also in the present invention, it is preferable that the
sheet resistance of the cathode containing the conductive
protection layer is constituted so as to be 20 .OMEGA./.quadrature.
or less.
[0020] Also in the present invention, it is preferable that the
anode is constituted so as to include any one of one kind or
combinations of two or more kinds of a metal group having a work
function of 4.5 eV or more, or alloys made of two or more kinds of
metals among the metal group having a work function of 4.5 eV or
more, or one kind or two or more kinds of conductive inorganic
oxides.
[0021] Also in the present invention, the anode may have a
structure in which a layer made of the metal or alloy and a layer
made of the conductive inorganic oxide are laminated in this order
from the base material side and is constituted so as to have the
light reflectiveness. Also, the anode may be made of the metal or
alloy and is constituted so as to have the light
reflectiveness.
[0022] According to the invention as mentioned above, the
conductive protection layer is interposed between the organic
layer, which contains the electron injecting layer and the organic
electroluminescent layer, and the cathode works so as to inhibit
the electron injecting layer of the organic electroluminescent
element from oxidizing owing to oxygen during the oxygen
introduction in the formation of the cathode or released from the
target.
[0023] According to the present invention, a structure in which a
conductive protection layer is interposed between an organic layer,
which contains an electron injecting layer and an organic
electroluminescent layer, and a cathode is taken, and the
conductive protection layer is made of a thin film made of at least
one kind of metal or a metal and a metal oxide thereof that is
formed according to a vacuum deposition method in which during
deposition process oxygen is not introduced. Accordingly, the
organic layer and the electron injecting layer are inhibited from
being oxidized not only in the deposition of the conductive
protection layer but also in the deposition of the cathode having
the optical transparency. As a result, an organic
electroluminescent element that is less in the characteristics
deterioration, high in the reliability and capable of taking out
light with high efficiency from a cathode of a top side to display
a high quality image can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a conceptual diagram of a fundamental
configuration showing an embodiment of an organic
electroluminescent (EL) element according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Hereinafter, an organic electroluminescent element of
present invention will be explained in detail.
[0026] The organic electroluminescent element of present invention
includes at least a base material, an anode, an organic
electroluminescent layer, a conductive protection layer having the
optical transparency and a cathode having the optical transparency
that are formed sequentially on the base material, the conductive
protection layer being made of a metal or a metal and a metal oxide
thereof.
[0027] Firstly, the organic electroluminescent element of present
invention will be explained with reference to the drawing as
follows.
[0028] FIG. 1 is a conceptual diagram of a fundamental
configuration showing an embodiment of an organic EL element
according to the invention. In FIG. 1, an organic EL element
includes a base material 1, with sequentially formed on the base
material 1, a first electrode (anode) 2, an organic layer 3
including an organic electroluminescent layer, an electron
injecting layer 4, a conductive protection layer 5 having the
optical transparency and a second electrode (cathode) 6 having the
optical transparency.
[0029] Hereinafter, configurations of the organic
electroluminescent element will be explained as follows.
[0030] 1. Base Material
[0031] Firstly, a base material 1 used in the present invention
will be explained as follows. As a material capable of being used
as the base material 1, as far as it has the self-supporting
properties, there is no particular restriction. Furthermore, in the
case of the base material 1 being disposed below the anode 2 of a
metal layer, there is no particular necessity of having the
transparency.
[0032] As the base material 1, for instance, quartz or glass,
silicon wafer, glass on which a TFT (thin film transistor) is
formed, polymer materials such as polycarbonate (PC), polyethylene
terephthalate (PET), polybutylene terephthalate (PBT),
polyphenylene sulfide (PPS), polyimide (PI), polyaiude imide (PAI),
polyether sulfone (PES), polyether imide (PEI) and polyether ether
ketone (PEEK) can be cited.
[0033] Among these materials, quartz, glass, silicon wafer, or
super-engineering plastics such as polyimide (PI), polyamide-imide
(PAI) polyether sulfone (PES), polyether imide (PEI) and polyether
ether ketone (PEEK) is preferable. These materials have the heat
resistance of 200.degree. C. or more and allow making a temperature
of the base material high in a manufacturing process of TFTs of an
active matrix driving display device. However, in the case of using
the polymer materials, in order to inhibit the organic layer 3 from
deteriorating owing to gas generated from the base material 1, it
is necessary to form a gas barrier layer made of silicon oxide or
silicon nitride at least on a formation surface facing the anode 2
of the base material 1. A thickness of the base material 1 can be
set in consideration of a material and application situations of an
image display device and can be set, for instance, in the range of
substantially 0.005 to 5 mm.
[0034] 2. First Electrode
[0035] As a first electrode (anode) 2 of the present invention that
constitutes an organic EL element, as far as it is formed of a
conductive material, there is no particular restriction, and, for
instance, metals such as Au, Ta, W, Pt, Ni, Pd, Cr, Cu and Mo, or
the metal oxides thereof, combinations of Al alloys, Ni alloys and
Cr alloys, or laminated bodies of these metallic materials can be
cited. Furthermore, conductive inorganic oxides such as In--Sn--O,
In--Zn--O, Zn--O, Zn--O--Al and Zn--Sn--O; conductive polymers such
as metal-doped polythiophene; and .alpha.-Si and .alpha.-SiC can be
cited.
[0036] The anode 2 plays a role of supplying holes to the organic
layer 3. Accordingly, it is preferable to use a conductive material
which work function is large. In particular, the anode 2 is
preferably comprised of at least one kind of metals having the work
function of 4.5 eV or more, or at least one kind of materials
contained in a group of alloys of these metals or conductive
inorganic oxides. Since the anode metal is easily oxidized when the
work function is less than 4.5 eV, the work function is preferably
4.5 eV or more.
[0037] A thickness of such anode 2, though depending on the
material, is preferably in the range of 40 to 500 nm. When the
thickness of the anode 2 is less than 40 nm, in some cases, the
electric resistance becomes higher; on the other hand, when the
thickness of the anode 2 exceeds 500 nm, owing to a step present at
an end portion of a patterned anode 2, in a upper layer (organic
layer 3, electron injecting layer 4, conductive protection layer 5
and cathode 6) a cut or disconnection may be caused, or the
short-circuit between anode 2 and cathode 6 may occur.
[0038] As a deposition method of the anode 2, a sputtering method,
a vacuum heating vapor deposition method, an EB deposition method
and an ion plating method can be cited. A value of the resistivity
is preferably 1.times.10.sup.-2 .OMEGA..multidot.cm or less, and
more preferably 5.times.10.sup.-4 .OMEGA..multidot.cm or less. In
order to suppress the circuit loss of electric power owing to
electrode resistance, the resistance is preferable to be lower.
[0039] 3. Organic Layer
[0040] An organic layer 3 of the present invention that constitutes
an organic EL element usually includes an organic
electroluminescent layer, a hole injecting and transporting layer,
a hole transporting layer, an electron transporting layer and so
on. The organic layer 3 in the invention like this necessarily
contains at least one layer of an organic electroluminescent layer.
Furthermore, the organic electroluminescent layer and the
abovementioned layers can be combined to form an organic layer 3
made of a plurality of layers.
[0041] Furthermore, as a method of forming the organic layer 3 on
the anode 2 used in the present invention, from the necessity of
patterning thereof, as far as it enables to form a high precisely
pattern, there is no particular restriction. For instance, methods
of forming an organic layer 3 in pattern by use of a vapor
deposition method, a printing method, or an ink jet method, methods
of coating a material that forms an organic layer 3 as a coating
solution such as a spin coating method, a casting method, a dipping
method, a bar coat method, a blade coat method, a roll coat method,
a gravure coat method, a flexo printing method, a spray coat method
and a self-organizing method (layer-by-layer self-assembled method,
self-assembled monolayer method) can be cited. Among these, in
particular, the organic layer 3 can be preferably formed by use of
a vapor deposition method, a spin coat method or an ink jet
method.
[0042] Like the present invention, when a conductive material made
of a metal as will hereinafter described is used as the conductive
protection layer 5, owing to a large work function (4.0 eV or
more), an energy barrier at an interface between the conductive
protection layer 5 and an organic electroluminescent layer becomes
higher; accordingly, under a low voltage it becomes difficult to
inject electrons directly from the conductive protection layer 5 to
the organic electroluminescent layer. Accordingly, it is preferable
to form a structure in which an electron injecting layer or an
electron injecting and transporting layer is disposed on the
conductive protection layer 5 side. The electron injecting layer
and the electron injecting and transporting layer, in order to take
out light efficiently from the cathode 6 of a top side, are
necessary to have sufficient optical transparency. The hole
injecting and transporting layer and the electron injecting and
transporting layer, respectively, may be formed in a lamination
structure in which an injection function layer and a transporting
layer are separately disposed.
[0043] (1)Organic Electroluminescent Layer
[0044] An organic electroluminescent layer used in the present
invention that constitutes the organic layer 3 will be explained as
follows.
[0045] An organic electroluminescent layer that constitutes the
organic layer 3 concurrently has functions below.
[0046] Injection function: a function of capable of injecting,
under an electric field, holes from the anode 2 or the hole
injecting layer, and electrons from the cathode 6 or the electron
injecting layer 4
[0047] Transporting function; a function of transporting injected
charges (electrons and holes) under a force of an electric
field
[0048] Emission function: a function of providing a place of
recombination of electrons and holes, and of leading this to
emission
[0049] As materials of an organic electroluminescent layer having
such functions, common materials so far known as light-emitting
layer materials of an organic EL element can be used without
particular restriction. For instance, metal complex dyes such as
tris(8-quinolinorate) aluminum complex (Alq3) and high molecular
weight materials such as polydialkylfluorene derivatives can be
preferably used.
[0050] A thickness of the organic electroluminescent layer, without
particular restriction, can be made for instance in the range of
substantially 10 to 200 nm.
[0051] In the organic of the present invention EL element, the
organic electroluminescent layer is an indispensable layer, and,
when a full color and a multi-color display are manufactured, the
layer is necessary to be patterned. As materials that form such a
light-emitting layer, normally, dye base, metal complex base or
polymer base luminescent materials can be cited. Hereinafter, as
materials that form such an organic electroluminescent Layer,
luminescent materials will be explained.
[0052] (i) Dye Base Materials
[0053] As the dye base materials, cyclopendamine derivatives,
tetraphenylbutadiene derivatives, triphenylamine derivatives,
oxadiazole derivatives, pyrazoloquinoline derivatives,
distyrylbenzene derivatives, distyrylarylene derivatives, silole
derivatives, thiophene cyclic compounds, pyridine cyclic compounds,
perynone derivatives, perylene derivatives, oligothiophene
derivatives, trifumanylamine derivatives, oxadiazole dimer,
pyrazoline dimer and others can be listed.
[0054] (ii) Metal Complex Base Materials
[0055] As metal complex base materials, metal complexes having a
structure that has, as central metal, Al, Zn, Be or a rare earth
element such as Tb, Eu and Dy and, as a ligand, oxadiazole,
thiadiazole, phenylpyridine, phenylbenzoimidazole and quinoline
structure such as aluminum quinolinol complex, benzoquinolinol
beryllium complex, benzoxazol zinc complex, benzothiazole zinc
complex, azomethyl zinc complex, porphyrin zinc complex, europium
complex, iridium metal complex, and platinum ,metal complex can be
cited.
[0056] (iii) Polymer Base Materials
[0057] As the polymer base materials, polyparaphenylene vinylene
derivatives, polythiophene derivatives, polyparaphenylene
derivatives, polysilane derivatives, polyacethylene derivatives,
polyfluorene derivatives, polyvinylcarbazole derivatives, and ones
obtained by polymerizing the above-mentioned dyes and metal complex
base luminescent materials can be cited.
[0058] (2) Hole Injecting and Transporting Layer, Hole Transporting
Layer
[0059] As the hole injecting and transporting layer, as far as the
layer can transport holes injected from the anode 2 into the
organic electroluminescent layer, there is no particular
restriction thereon. For instance, it may be formed of any one of a
hole injecting layer that has a function of stably injecting holes
injected from the anode 2 into the organic electroluminescent
layer, a hole transporting layer that has a function of
transporting holes injected from the anode 2 into the organic
electroluminescent layer, or a combination thereof, or a layer that
has both functions.
[0060] Furthermore, as a thickness of the hole injecting and
transporting layer, as far as a function thereof can be fully
exhibited, there is no particular restriction. However, it is in
the range of 10 to 300 nm and preferably in the range of 30 to 100
nm.
[0061] As a material of such a hole injecting and transporting
layer, as far as it allows stably transporting holes injected from
the anode 2 to the organic electroluminescent layer, there is no
particular restriction. Specifically, N-(1-naphtyl)-N-phenylbenzine
(.alpha.-NPD) 4,4,4-tris (3-methylphenylphenylamino) triphenylamine
(MTDATA), and polymers such as poly3,4 ethylenedioxythiophene
(PEDOT), polyvinyl carbazole (PVCz), polyaniline derivatives, and
polyphenylene vinylene derivatives can be cited. As a hole
transport compound, any one of known compounds that have been so
far used in the hole injecting and transporting layer of the
organic EL element can be selected and used.
[0062] (3)Electron Injecting Layer
[0063] Furthermore, as a material of the electron injecting layer
4, oxides and fluorides of alkali metals and alkali earth metals
(for instance, LiF, NaF, LiO.sub.2, MgF.sub.2, CaF.sub.2, and
BaF.sub.2) and so on can be cited. Among these, fluorides of alkali
earth metals (MgF.sub.2, CaF.sub.2 and BaF.sub.2) can be more
preferably used in view of capability of improving the stability
and life of the organic layer 3. This is because since fluorides of
alkali earth metals are low in the reactivity with water in
comparison with that of compounds of alkali metals and oxides of
alkali earth metals, during deposition, or after the deposition,
the fluorides of alkali earth metals less absorb water.
Furthermore, this is because the fluorides of alkali earth metals
are higher in the melting point in comparison with that of
compounds of alkali metals, that is, excellent in the heat
resistance.
[0064] A thickness of the electron injecting layer 4, since the
oxides and fluorides of alkali metals and alkali earth metals are
insulative, is preferably in the range of substantially 0.2 to 10
nm.
[0065] Furthermore, when, other than the electron injecting layer
4, a metal having a work function of 4.0 eV or less is disposed as
an electron injecting layer 4, electrons can be more easily
injected. Specific examples include Ba, Ca, Li, Cs, Mg and so on.
In the case of an electron injecting layer 4 constituted of such
metals being formed, a film thickness thereof is in the range of
0.2 to 50 nm and more preferably in the range of 0.2 to 20 nm. This
is because from the necessity of taking out light from a
transparent electrode of a top side, the electron injecting layer 4
is also required to be transparent.
[0066] Still furthermore, as the electron injecting and
transporting layer, a metal-doped layer where an alkali metal or
alkali earth metal is doped in an electron transporting organic
material can be formed. As the electron transporting organic
materials, for instance, bathocuproin (BCP), bathophenanthroline
(Bphen) and so on can be cited, and as the doping metals, Li, Cs,
Ba, Sr and so on can be cited. A molar ratio of the electron
transporting organic material and the metal in the metal-doped
layer is in the range of 1:1 to 1:3 and preferably in the range of
substantially 1:1 to 1:2. A thickness of the electron injecting and
transporting layer made of such metal-doped layer, since the
electron mobility is large and the optical transparency is higher
than that of the metal, is in the range of 5 to 500 nm, and
preferably in the range of substantially 10 to 100 nm.
[0067] (4)Electron Transporting Layer
[0068] As a material that constitutes an organic electron
transporting layer, as far as it can transport electrons injected
from the electron injecting layer 4 into a light-emitting layer,
there is no particular restriction. Specifically, as the electron
transporting organic material, Alq (aluminum quinolinol complex),
BCP (bathocuproin) or Bphen (bathophenanthroline) can be cited.
[0069] (5)Conductive Protection Layer
[0070] The conductive protection layer 5 has both of a function of
transporting electrons and a function of protecting (protection
from the deposition processes such as sputtering, EB, ion plating
and so on) the electron injecting layer 4 and the organic layer 3
in the process of depositing a transparent electrode for forming
the cathode 6. When a transparent electrode is formed on the
electron injecting layer 4 by the sputtering method, since the
electron injecting layer 4 and the organic layer 3 are exposed to
an impact of Are having high energy of several hundred volts, a
structure of the organic electroluminescent layer is changed, and
in the electron injection at an interface between the organic
electroluminescent layer and the transparent electrode,
radiationless quenching is caused to result in deteriorating the
luminescent characteristics. Furthermore, in the case of the
electron injecting layer 4 being formed of an alkali metal or an
alkali earth metal, the electron injecting layer 4 is likely to be
oxidized, and, owing to oxygen introduction in the formation
process of an electrode such as ITO and IZO in the sputtering or
oxygen release from a target, a metal that is used in the electron
injecting layer 4 is oxidized, and thereby, in some cases, the
electron injecting function may be lost. When the conductive
protection layer 5 is disposed between the electron injecting layer
4 and a second electrode 6 with an intention of protecting the
electron injecting layer 4 and the organic layer 3, sputter damage
of the electron injecting layer 4 and the organic layer 3 can be
alleviated, and thereby the emission efficiency and the durability
of the organic EL element can be improved.
[0071] The conductive protection layer 5 is a thin film made of at
least one kind of optically transparent metals that is formed
according to a vacuum deposition method in which oxygen is not
introduced during the deposition process, and may be a
multi-layered film made of two or more kinds of metals or a film in
which two or more kinds of metals are mixed. Furthermore, the
conductive protection layer 5 may be a thin film made of an
optically transparent metal and a metal oxide thereof. In the case
of a thin film made of a metal oxide being contained, a thin film
of the metal oxide is preferably disposed on a side of cathode 6.
Still furthermore, in the conductive protection layer 5, a
plurality of metals that constitutes the metal oxide may be
alloyed.
[0072] As the metals, in order to make the light transmittance in
the visible region of the metal film 50% or more, when the
extinction coefficient of a metal is expressed with k, a film
thickness with d, and a wavelength with .lambda., a range of
0.ltoreq.k.times.d<0.11.lambda. is preferable. Also, the value
of the extinction coefficient as k is determined by measuring the
material formed on silicon wafer with ellipsometer. Further, the
band gap of the metal oxide contained in the conductive protection
layer 5 is preferable to be 2.9 eV or more. These metals and metal
oxides thereof are not restricted as far as it satisfies
above-mentioned conditions, for instance, metals such as zinc,
lead, tin, indium, gallium, magnesium, aluminum, gold and silver,
and the metal oxides thereof can be cited. Furthermore, after a
conductive protection layer made of only a metal is formed, when an
oxidation process is applied to the protective layer, the band gap
of the conductive protection layer 5 has to become 2.9 eV or
more.
[0073] It is because when the band gap is less than 2.9 eV, the
metal oxide is colored and lowers the transmittance in the visible
region. As the aforementioned oxides of metals, for instance,
oxides such as Sn--O, In--O, In--Sn--O, In--Zn--O, Zn--O, Ga--O,
Zn--Sn--O and Ga--In--O can be cited.
[0074] A thickness of the conductive protection layer 5 having the
characteristics is preferably selected to satisfy the relational
expression of 0.ltoreq.k.times.d<0.11.lambda.. In general, in
the case of a thin film being made of a metal, in the range of 5 to
30 nm and preferably in the range of substantially 5 to 20 nm, and
in the case of a thin film being made of a layer containing metal
oxide, in the range of 5 to 300 no and preferably in the range of
substantially 10 to 100 nm.
[0075] As the vacuum deposition method for forming the conductive
protection layer 5, a resistance heating deposition method, an ion
beam deposition method, a sputtering method, an ion plating method
and so on can be cited.
[0076] (6)Second Electrode
[0077] The second electrode (cathode) 6, as long as it is formed of
a transparent and conductive material, is not particularly
restricted. As the transparent and conductive materials, conductive
oxides such as In--Sn--O, In--Zn--O, Zn--O, Zn--O--Al and Zn--Sn--O
can be cited.
[0078] A thickness of the cathode 6 like this is preferably in the
range of 10 to 500 nm, and the transmittance in the visible region
of 380 to 780 nm is preferably 50% or more. When the thickness of
the cathode 6 is less than 10 nm, the conductivity becomes
insufficient, and when the thickness of the cathode 6 exceeds 500
nm, the optical transparency becomes insufficient and furthermore
when during the manufacturing process or after the manufacture of
an organic EL element it is deformed, defects such as crack and so
on are unfavorably likely to be generated to the cathode 6.
[0079] Furthermore, the sheet resistance of the cathode 6 including
the conductive protection layer 5 is preferably 20
.OMEGA./.quadrature. or less.
[0080] The cathode 6 can be formed by vacuum deposition methods
such as a sputtering method, anion plating method and an electron
beam method. In the formation of the cathode 6 like this, the
conductive protection layer 5 inhibits the electron injecting layer
4 from being oxidized owing to oxygen introduction or oxygen
released from the target, and thereby the electron injection
characteristics to the organic layer 3 can be inhibited from
deteriorating.
[0081] (7)Others
[0082] In the present invention, on the cathode 6, color filter
layers and/or color conversion phosphor layers may be disposed to
correct light of the respective colors and thereby heighten the
color purity.
[0083] As the color filter layers, for instance, a blue-colored
layer, a red-colored layer and a green-colored layer, respectively,
may be formed with resin compositions prepared by dispersing one
kind or a plurality of kinds of pigments such as azo,
phthalocyanine and anthraquinone base pigments in a photosensitive
resin.
[0084] Furthermore, the color conversion phosphor layers can be
formed as follows for instance. That is, a coating solution in
which a desired fluorescent dye and a resin are dispersed or
solubilized is coated according to a method such as a spin coat,
roll coat or cast coat to form a film, the film is patterned
according to a photolithography method, and thus the respective
layers of a red conversion phosphor layer, a green conversion
phosphor layer andablue conversion phosphor layer can be
formed.
[0085] It is to be noted that the present invention is not limited
to the above-described embodiment. The above-described embodiment
is only illustrative. The changes or modifications that have
substantially the same constructions as those which are made using
the technical ideas described in the claimed scope of the present
invention and exhibit the same functions and effects are included
in the technical scope of the present invention whatever kinds they
may be of.
EXAMPLES
[0086] The present invention will be detailed with reference to
examples as follows.
Example 1
[0087] As a base material, a 40 mm.times.40 mm-transparent glass
substrate (non-alkali glass NA35, manufactured by NH Techno glass
Corp.) having a thickness of 0.7 mm was prepared, after the
transparent glass substrate was washed according to a standard
process, a thin film of Ag (100 nm thick) was deposited by a
magnetron sputtering method. When the thin film of Ag was formed,
Ar was used as a sputtering gas, a pressure was set at 0.15 Pa, and
a DC output was set at 200 W. Next, on the Ag thin film, in order
to give a role of accelerating hole injection, a thin film (30 nm
thick) of indium tin oxide (ITO) was formed by use of a magnetron
sputtering method. In the formation of the ITO thin film formation,
a gas mixture of Ar and O.sub.2 (volume ratio Ar: O.sub.2=100: 1)
was used as a sputtering gas, a pressure was set at 0.1 Pa and a DC
output was set at 150 W.
[0088] Subsequently, on the anode, a photosensitive resist (trade
name OFPR-800, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was
coated, followed by mask exposure, development (NMD3 manufactured
by Tokyo ohka Kogyo Co., Ltd. was used) and etching, and thereby
the anode was formed in pattern.
[0089] Next, the transparent glass substrate with the anode was
washed and subjected to UV ozone treatment, thereafter in air
polyethylene dioxythiophene-polystyrene sulfonate (PEDOT-PSS)
expressed by the following structural formula (1) was coated by a
spin coating method so as to cover the anode on the transparent
glass substrate, followed by drying, and thereby a hole injecting
and transporting layer (80 nm thick) was formed. 1
[0090] (In the above, n is a number in the range of 10,000 to
500,000.)
[0091] Next, in a globe box in a state of low oxygen (oxygen
concentration is 1 ppm or less) and low humidity (water vapor
concentration is 1 ppm or less), on the hole injecting and
transporting layer,
poly(dioctyldivinylenefluorene-co-anthracene)(PF) expressed by the
following structural formula (2) was coated according to a spin
coating method, dried and thereby a light-emitting layer (80 nm
thick) was formed. 2
[0092] (In the above, n is a number in the range of 100,000 to
1,000,000.)
[0093] Furthermore, on the light-emitting layer, Ca was vapor
deposited with a thickness of 5 nm, and thereby an electron
injecting layer was formed. Deposition conditions were as follows.
That is, a vacuum pressure was set at 5.times.10.sup.-5 Pa and a
film deposition rate was set at 1 .ANG./sec.
[0094] On the electron injecting layer, Sn (refractive index as n
is 4.7, extinction coefficient as k is 1.6@1000 nm) was vacuum
deposited with a thickness of 20 nm to form a conductive protection
layer. Deposition conditions were as follows. That is, a vacuum
pressure was set at 5.times.10.sup.-5 Pa and a film deposition rate
was set at 1 .ANG./sec.
[0095] Next, by a magnetron sputtering method, an ITO thin film
(100 nm thick) was deposited to form a cathode. In the formation of
the ITO thin film, a gas mixture of Ar and O.sub.2 (volume ratio
Ar: O.sub.2=200: 1) was used as a sputtering gas, a pressure was
set at 5.5.times.10.sup.-2 Pa, a DC output was set at 150 W and a
film deposition rate was set at 4 .ANG./sec.
[0096] Furthermore, on a transparent glass substrate, under
conditions same as the above, on a Sn thin film, ITO was separately
formed, and this was measured, under the conditions below, of the
resistivity and the transmittance in the visible region of 380 to
780 nm. As a result, a surface resistance value of the ITO thin
film containing a Sn thin film was 18 .OMEGA./.quadrature.. The
average transmittance in the visible region was substantially
60%.
[0097] (Measurement of Surface Resistance)
[0098] The surface resistance value (.OMEGA./.quadrature.) was
measured according to a four-probe method with Loresta-GP
manufactured by Mitsubishi Chemicals Inc.
[0099] (Measurement of Resistivity)
[0100] The measured surface resistance value (.OMEGA./.quadrature.)
was multiplied by a film thickness (cm) and thereby the resistivity
value (.OMEGA..multidot.cm) was calculated. As a film thickness, a
film section was measured with Nanopics 1000 manufactured by Seiko
Instruments Inc.
[0101] (Measurement of Light Transmittance)
[0102] The light transmittance was measured at room temperature in
air by use of a UV-visible spectrophotometer (UV-2200A manufactured
by Shinadzu Corporation).
[0103] Thereafter, in a globe box in a state of low oxygen (oxygen
concentration is 1 ppm or less) and low humidity (water vapor
concentration is 1 ppm or less), sealing was performed with
non-alkali glass.
[0104] Thereby, an organic EL element that has an anode patterned
in lines with a width of 2 mm; an electron injecting layer, a
conductive protection layer and a cathode that are formed in lines
with a width of 2 mm so as to be orthogonal to the anode; and four
light-emitting areas (area of 4 mm.sup.2) was prepared.
[0105] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 200
mA/cm.sup.2, and brightness of the light-emitting area measured
from a top (cathode) side was 12000 cd/n.sup.2.
[0106] From the results of the current density and brightness
characteristics, it was confirmed that owing to the presence of the
conductive protection layer made of a Sn thin film, oxidation of
the light-emitting layer and the electron injecting layer due to
oxygen introduction during the formation of the cathode and damage
in the sputtering were inhibited from occurring.
Example 2
[0107] Except that as a conductive protection layer, instead of the
Sn thin film, an In (refractive index as n is 1.019, extinction
coefficient as k is 2.08@500 nm) thin film (20 nm thick) was
deposited under the same conditions, similarly to example 1, an
organic EL element was prepared.
[0108] Similarly to example 1, the surface resistance value of an
ITO film including the In thin film was measured and found to be 18
.OMEGA./.quadrature.. Furthermore, similarly to example 1, the
light transmittance in the visible region of 380 to 780 nm was
measured and found that average transmittance over the visible
region was substantially 70%.
[0109] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 190
mA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 12000 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that owing to the presence of the conductive protection layer made
of the In thin film, oxidation of the light-emitting layer and the
electron injecting layer due to oxygen introduction during the
formation of the cathode and damage during the sputtering were
inhibited from occurring.
Example 3
[0110] Except that as a conductive protection layer, in place of
the Sn thin film, azn (refractive index as nis 0.773, extinction
coefficient as k is 3.912@545 nm) thin film (20 nm thick) was
formed by a vacuum deposition method (vacuum pressure:
5.times.10.sup.-5 Pa, and film deposition rate: 1.0 .ANG./sec),
similarly to example 1, an organic EL element was prepared.
[0111] Similarly to example 1, the surface resistance value of the
ITO film including the Zn thin film was measured and found to be 19
.OMEGA./.quadrature.. Furthermore, similarly to example 1, average
transmittance over the visible region of the ITO including the Zn
thin film was measured and found to be substantially 70%.
[0112] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 190
mA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 12000 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that owing to the presence of the conductive protection layer made
of the Zn thin film, oxidation of the light-emitting layer and the
electron injecting layer due to oxygen introduction during the
formation of the cathode and damage during the sputtering were
inhibited from occurring.
Example 4
[0113] Except that as a conductive protection layer, in place of
the Sn thin film, a Pb (refractive index as nis 1.68, extinction
coefficient as k is 3.67700 nm) thin film (20 nm thick) was formed,
similarly to example 1, an organic EL element was prepared.
[0114] Similarly to example 1, the surface resistance value of an
ITO film including the Pb thin film was measured and found to be 15
.OMEGA./.quadrature.. Furthermore, similarly to example 1, average
visible transmittance in the visible region of 380 to 780 nm of the
ITO including the Pb thin film was measured and found to be
substantially 60%.
[0115] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 200
mA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 11000 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that owing to the presence of the conductive protection layer made
of the Pb thin film, oxidation of the light-emitting layer and the
electron injecting layer due to oxygen introduction during the
formation of the cathode and damage during the sputtering were
inhibited from occurring.
Example 5
[0116] Except that as a conductive protection layer, Sn (20 nm
thick) was formed, and as the second electrode (cathode), instead
of the ITO film, a thin film of indium zinc oxide (IZO) that is an
inorganic oxide was formed, similarly to example 1, an organic EL
element was prepared. As a sputtering gas, only Ar was used, a
pressure was set at 5.5.times.10.sup.-2 Pa, a DC output was set at
150 W, and a film deposition rate was set at 4 .ANG./sec.
[0117] Similarly to example 1, the surface resistance value of an
ITO film including the Sn thin film was measured and found to be 19
.OMEGA./.quadrature.. Furthermore, similarly to example 1, average
transmittance over a visible region of the IZO thin film including
the Sn thin film was measured and found to be substantially
70%.
[0118] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 210
mA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 12000 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that owing to the presence of the conductive protection layer made
of the Sn thin film, oxidation of the electron injecting layer due
to oxygen introduction during the formation of the cathode and
damage during the sputtering were inhibited from occurring.
Comparative Example 1
[0119] Except that a conductive protection layer was not formed,
similarly to example 1, an organic EL element was prepared.
[0120] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 30
mA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 2000 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that in an element in which a conductive protection layer was not
formed, owing to oxidation of the electron injecting layer due to
oxygen during the formation of the cathode, the emission
characteristics were deteriorated.
Example 6
[0121] Firstly, similarly to example 1, an anode was formed on a
transparent glass substrate, followed by exposing the transparent
glass substrate with the anode under oxygen plasma, further
followed by forming a hole transporting layer (50 nm thick) made of
bis(N-naphtyl)-N-phenylbe- nzidine (.alpha.-NPD) expressed by the
following structural formula (3) by vacuum heating vapor deposition
method on the transparent glass substrate so as to cover the anode.
The deposition conditions of the hole transporting layer were set
such that vacuum pressure was 5.times.10.sup.-5 Pa, the film
deposition rate was 3 .ANG./sec, and the heating temperature was
350.degree. C. 3
[0122] Next, according to the vacuum deposition method, on the hole
transporting layer, tris(8-quinolirate)aluminum complex (Alq3)
expressed by the following structural formula (4) was deposited and
thereby a light-emitting layer (60 nm thick) was formed. The
deposition conditions of the light-emitting layer were set such
that vacuum pressure was 5.times.10.sup.-5 Pa and the film
deposition rate was 3 .ANG./sec. 4
[0123] Furthermore, by the vacuum deposition method, on the
light-emitting layer, a co-deposition layer of bathocuproin (BCP)
expressed by the following structural formula (5) and Li was
formed, and thereby an electron injecting layer (20 nm thick) was
formed. The deposition conditions were set such that the vacuum
pressure was 5.times.10.sup.-5 Pa and the film deposition rate of
the respective materials was 3 .ANG./sec. 5
[0124] Subsequently, similarly to example 1, a conductive
protection layer Sn and a cathode ITO were formed, followed by
finally sealing with sealing glass.
[0125] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 40
mA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 3000 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that owing to the presence of the conductive protection layer made
of Sn thin film, oxidation of the electron injecting layer due to
oxygen during the formation of the cathode and damage during the
sputtering were inhibited from occurring.
Comparative Example 2
[0126] Except that a conductive protection layer was not formed,
similarly to example 6, an organic EL element was prepared.
[0127] A current density when a voltage of 6 V was applied between
an anode and a cathode of the organic EL element was 2.8
MA/cm.sup.2, and brightness of a light-emitting area measured from
a top (cathode) side was 160 cd/m.sup.2. From the results of the
current density and brightness characteristics, it was confirmed
that in the element in which a conductive protection layer was not
formed, oxidation of the electron injecting layer due to oxygen
during the formation of the cathode and damage during the
sputtering were not inhibited from occurring.
* * * * *